Nellemann estimates that taxation has quickly become "the largest share of ISIL's income, both through taxation schemes of the local populous," various mafia-like schemes forcing payment with the threat of violence, as well as human trafficking. The expert suggested that "in 2015, [the smuggling] business is likely going to exceed a total of $2 billion, of which the Islamic State will slowly increase their share."

In its online English magazine, Dabiq, ISIS lays out its justification for its brutality against the Yazidis on religious grounds:

"Enslaving the families of the kuffar [unbelievers] and taking their women as concubines is a firmly established aspect of the Shariah [Islamic law] that if anyone were to deny or mock, he would be denying or mocking the verses of the Qur'an and the narrations of the Prophet."